The transport of a test species from a sample to a receiver solution against its concentration gradient across a membrane is well-known in biological chemistry. Such uphill transport processes are used in analytical chemistry, but they have almost exclusively dealt with inorganic ions. Donnan dialysis, where an ionic strength gradient is the driving force, is the most common of these methods. The present study will extend analytical applications of uphill transport to biomolecules through the development of sustained passive diffusion as a driving force. Here, a reaction at the receiver-membrane interphase will maintain a flux of the test species that is independent of its total concentration in the receiver. The two means that will be investigated to sustain the diffusional flux are interaction of the test species with micelles and alternation of the chemical state of the test species by an acid-base reaction in the receiver solution. The former, which has not been studied, is applicable to all hydrophobic species. The test compounds will include aromatic amines, fatty acids, selected amino acids, polypeptides, phenols and polychlorinated biphenyls. These are of interest to either biological or environmental chemistry. For most work, ionic surfactants will be used. With polypeptides, nonionic detergents will be tested to avoid denaturization even though for purely analytical work this is inconsequential as electrochemical analysis will be used. The acid-base driven transport is complementary; although it is not applicable to neutral compounds, it does not have a requirement of hydrophobicity. The methods will be optimized to provide fluxes that are independent of time, directly proportional to the initial concentrations of test species in the sample, and sufficiently rapid to yield practical preconcentration factors. Among the variables will be the nature of the membrane. Here, there are two questions, namely, ion-exchange vs. neutral membranes and the role of nonspecific interactions between aromatic test species and the membrane backbone. The latter will be evaluated by measuring the activation energy of transport under various conditions. Improved benchtop analytical chemistry from lower detection limits and less interference is the initial outcome that is projected. The long term goals include the development of improved microdialysis systems for in vivo samplers, membrane-based units for the continuous recovery of targeted species from bioreactors, and flow-systems for monitoring and treating wastewater.